Vaillant boiler breaking down -- impossible to order replacement parts because of unique supplier

Last month, our Vaillant boiler started making strange airplane take-off noises from time to time. See:

https://www.youtube.com/watch?v=yjyI8D03zII

and:

https://www.youtube.com/watch?v=EnOoDrUyHkc

The local council was coming buy to do their periodic inspection and found the boiler's emissions were well within tolerances.  They suggested we get an accredited chimney sweep also "SSIGA" certified to clean gas boilers, which I did, selecting one from the following list:

https://m4.ti.ch/fileadmin/DT/temi/domande_costruzione/polizia_fuoco/Elenco_spazzacamini_08112017.pdf

That gentleman came, opened the boiler and began performing his cleaning.

While he was doing his cleaning, the heat exchanger coil broke, beginning to spurt water from the bottom left in the picture above.

Time to call our trusted plumber.  Our plumber looked at repairing this coil as a temporary fix, but was unable to because of the mix of metals used in the heat exchanger tube.  No problem -- let's look at ordering the part.

I contacted https://www.vaillant.ch/ only to find out that they only sell parts to approved heating installers.  No problem -- I'll get my plumber to order the part.

Here's the problem: In Switzerland Vaillant appears as far as I can tell to deal with a single, specific installer in each region.  And in my region, the installer/supplier is the same one that gave us grief and poor service last time we had a problem.  And furthermore, they seem to keep a record of who owns what where, and instead of being willing to give me plumber a reasonable price for the replacement boiler, they looked up where we lived, looked up who we are, and seemed to indicate there might be a problem getting the part.  Making it difficult for him, they'll only sell him the part if he turns up in person, with cash.

It turns out the heat exchanger is not one of the parts they replaced when they charged us CHF 2500 in 2018.  We asked about just the heat exchanger and they quoted CHF 994.50 including VAT (GBP. 764) -- "if they can get it."

In the UK, I can look up the equivalent part and simply order myself as a private individual from:
https://www.plumbnation.co.uk/boiler-spares/product/vaillant-heat-exchanger-dhw-6-coil-0020135133/ for GBP 500.92 (including VAT). "Next Working Day Delivery available on orders placed before 3pm."

We asked about order a whole new boiler, and they quoted CHF 4999.00. (GBP 3860.83). This is compared to buying one new for GBP 1191.26 + VAT ( CHF 1542.44) in the UK https://www.plumbnation.co.uk/site/vaillant-ecotec-plus-system-boiler-packs-erp/.

Apparently, this more than double the price is justified because the Vaillant-appointed regional supplier must come out to do the final "start up" of the product?  To be clear, I have my own, certified plumber who would do the install.  Why would VezzoliGas SA feel the need to quote a price which involves them somehow coming to our house to be involved in the final installation process?

I can't believe Vaillant boilers in the UK are any less rigorously tested than those in Switzerland (are they?) Why does Vaillant head office in Germany allow its regional subsidiary in Switzerland to limit supply to parts in such a way that there is a regional monopoly on prices by a single supplier?  It feels as though this supplier looks up where you live and decides how much they can charge you based on your neighbourhood and their past history with you.

On the grand scale of the cosmos, it's not a big deal.  But as a consumer it's a really unfortunate situation that will lead to me switching to a different boiler manufacturer.  Not necessarily because it's a better product, but just because it allows me to break out of the monopoly that Vaillant has allowed one particular (unhelpful) supplier to create over their parts and products in the area where I live.